Chronic kidney disease (CKD) eventually progresses to a stage where the kidneys can no longer adequately filter waste products and excess fluid from the blood. When this happens, life-sustaining hemodialysis becomes necessary to cleanse the blood. Hemodialysis involves drawing blood out, passing it through a machine to remove toxins and rebalance electrolytes, and then returning the cleaned blood to the body. Performing this process safely requires reliable, long-term access to the patient’s bloodstream.
The Necessity of High-Flow Vascular Access
Standard veins near the skin’s surface cannot withstand the high demands of hemodialysis treatment. The dialysis machine must process blood at high speeds to efficiently filter the entire blood volume multiple times per session. Standard protocol requires flow rates between 300 and 400 milliliters per minute. To prevent recirculation, the access point must sustain a flow volume often exceeding 500 milliliters per minute.
Peripheral veins cannot tolerate the repetitive needle insertions or the sustained high pressure and flow rate required for this therapy. Using standard veins would quickly lead to damage, collapse, and pain. For patients needing immediate dialysis, a temporary central venous catheter (CVC) is sometimes used, but these are not sustainable for long-term care. CVCs carry a higher risk of complications, including infection and blood clots.
The necessity of a permanent, robust access point led to the development of specialized surgical connections, often referred to broadly as a “shunt.” These permanent accesses are designed to withstand the physical demands of high-volume blood flow and repeated needle punctures over years of treatment. They provide a durable site that minimizes complications associated with temporary access methods. Creating this durable, high-flow access is a precondition for beginning long-term hemodialysis.
Defining the Permanent Dialysis Shunt
The term “shunt” refers to the two main types of permanent access created for hemodialysis: the arteriovenous (AV) fistula and the AV graft. Both are surgically constructed to connect an artery (carrying high-pressure blood) to a vein (carrying low-pressure blood). This connection achieves the necessary high flow rate by rerouting arterial blood directly into the venous system.
The arteriovenous fistula is the preferred method because it utilizes only the patient’s native blood vessels. A surgeon directly connects an artery to a neighboring vein, typically in the arm, without introducing foreign material. Since the fistula is made entirely of the patient’s own tissue, it has the lowest long-term risk of complications, including infection and clotting. Fistulas are known for their longevity, often functioning for many years.
An arteriovenous graft is used when a patient’s veins are too small or weak to support a native fistula. The graft connects an artery and a vein using a synthetic tube, most commonly made from expanded polytetrafluoroethylene (ePTFE). This prosthetic conduit acts as the bridge between the two vessels and is the site where the dialysis needles are inserted. Grafts carry a higher risk of infection and tend to have a shorter lifespan than native fistulas due to the foreign material involved.
Surgical Creation and Site Maturation
Creating the permanent dialysis access is a minor surgical procedure, typically performed on an outpatient basis using local anesthesia. The goal is to create an anastomosis, or connection, between a selected artery and a vein, usually in the forearm or upper arm. For an AV fistula, the high-pressure arterial blood flow is diverted into the low-pressure vein, a process called arterialization.
The vein reacts to this increased pressure and flow by changing structurally, meaning the access site is not ready for immediate use after surgery. The vein wall thickens and the vessel diameter enlarges significantly, making it durable and large enough to accommodate the wide-bore dialysis needles. This biological adaptation is known as maturation.
Fistula maturation is a physiological process that requires time, often taking a minimum of six weeks, and commonly two to four months before the access is ready. A fully mature fistula should have a diameter greater than 0.6 centimeters and a blood flow rate exceeding 600 milliliters per minute. The maturation period is shorter for an AV graft, which can usually be used within two to four weeks. This is because the synthetic tube is a fixed size and does not rely on the body’s natural adaptation. If a fistula fails to mature, a patient may require a secondary procedure or the creation of an AV graft.
Daily Care and Monitoring of the Access Site
Patient involvement in the daily care and monitoring of the dialysis access site is important for its long-term function and patency. A primary rule is protecting the access limb from any activity that could restrict blood flow or cause damage. This includes never allowing blood pressure to be measured on the access arm and avoiding tight clothing, jewelry, or heavy lifting that could compress the site. Patients should also avoid sleeping directly on the access limb.
A simple, daily check for the patency of the access involves feeling for the “thrill” and listening for the “bruit.” The thrill is a distinct vibration or buzzing sensation felt over the access site, caused by the turbulent, high-volume blood flow. The bruit is the corresponding swishing sound heard by placing an ear or stethoscope over the shunt. Both the thrill and the bruit confirm that blood is flowing properly through the connection.
Any noticeable change in these sensations, such as the thrill becoming weaker or disappearing, is a serious sign that a blood clot may be forming and requires immediate medical attention. Other signs of a potential problem include localized swelling, redness, warmth, or pain around the access site, which may indicate an infection. Prolonged bleeding after a dialysis session or a change in the temperature or color of the hand on the access side should also be reported promptly.